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January 14, 2010

Canine Genetics Explain Shar-pei Wrinkles

by Sam Savage

Scientists believe they have the answer to why the Chinese Shar-pei dog breed has a wrinkled appearance.

In the analysis of ten pedigree dog breeds, scientists have discovered 155 unique locations in the animals' genetic code that may play a role in giving a dog its distinct appearance. In the Shar-pei, researchers found differences in the HAS2 gene which makes an enzyme known to be important in the production of skin.

Joshua Akey, from the Department of Genome Sciences at the University of Washington in Seattle, explained to the BBC that there may have been a mutation in the gene at one time that led to a wrinkled puppy and someone probably decided to selectively breed that trait.

The pedigree dog is a very useful research tool in the study of genetics. The domestication of the grey wolf more than ten thousand years ago, and the selective breeding that arose, has resulted in more than 400 breeds of domestic dog. Each breed is very unique.

The causes of breed specific traits are easy to find when scientists compare the genetics of different groups. Scientists are also using genetic studies in dogs to find faulty genes that cause disease in both dogs and humans. The genetic makeup of dogs also gives helpful insight into how evolution works at the molecular level.

The research, led by Dr Akey, consisted of studying 32 wrinkled and 18 smooth Shar-peis. They compared specific areas of their DNA with that of other breeds. The team discovered four small differences in the genetic makeup of the two skin types of the Shar-pei in contrast to other breeds. These small, but significant, differences are called single nucleotide polymorphisms. The SNPs were located in the HAS2 gene.

"HAS2 makes hyaluronic acid synthase 2, and it's an enzyme that makes hyaluronic acid, and that's one of the principal constituents of the skin," explained Dr Akey.

In some rare cases, this gene sequence leads to severe wrinkling in human skin as well. "So, that suggested it was a good candidate to look at; and sure enough, when we sequenced it we saw that that gene explained wrinkling in Shar-peis," he told BBC News.

The research has also helped the team breakthrough into other areas of dog genetics to offer an understanding of why pedigree animals look the way they do.

Dr Akey said he was excited to have found five unique genes in the five-year study that contributed to the vast diversity found in dog breeds. "So our study found all five of those genes and then we found 150 new targets to explore. It's a powerful approach to look at the genetic legacy of selective breeding," he added.

Dr Akey and colleagues reported their findings in the Proceedings of the National Academy of Sciences (PNAS).